1. Field of the Invention
The present invention relates to a stator coil for a stepping motor, and particularly to the construction of the lead wire layout of the stator coil.
2. Background of the Invention
A conventional stepping motor includes two stator sections provided around a permanent magnet rotor. Each of the stator sections includes an annular coil and at least two yokes for generating alternate magnetic poles inside the annular coil. The coil is wound on a bobbin. Three lead wires are connected to the ends and to an intermediate tap of the coil through terminals. The coil and the connections of the coil and the lead wires are molded together with synthetic resin for the purpose of fixedly holding the connections, water-proofing the coil and the connections, and so forth. At the time of the molding as shown in FIG. 6, the three lead wires A, B and C are juxtaposed around the coil along its circumference and are then embedded together in a single holding projection D by the molding. The coil is thereafter combined with the yokes to constitute the stator section. Both stator sections are juxtaposed in the axial direction of the stepping motor. The lead wires for each coil are then led out in a single axial direction.
In the conventional stepping motor, the terminals are often displaced and short-circuited to each other due to the pressure of the molding, so that the yield for the production of the stepping motor is low.
In order to reduce such short circuit problems, sufficient distance between the terminals must be maintained. To increase the distance, the circumferential length of the holding projection D must be increased. In order to lay the lead wires for each coil out in the single axial direction, since both the coils are juxtaposed in the axial direction of the stepping motor, the holding projections D for both the coils need to be disposed in positions different from each other in the circumferential direction of the stepping motor, as shown in FIG. 6. A space extending in the axial direction of the stepping motor and having a circumferential length equal to the sum of the circumferential lengths of both the holding projections needs to be provided in a motor housing in which the coils are housed. For that reason, the size of the stepping motor must be quite large. The conventional stepping motor has such a problem of large size.